1. Field of the Invention
The present invention relates to a liquid crystal display process, and more particularly, to a method of forming a thin film transistor on a transparent plate.
2. Description of the Related Art
Active matrix LCDs (Liquid Crystal Displays) have been developed for mass production. The active matrix LCDs are highly integrated circuits whose level of integration is enhanced by using a technique of producing a semiconductor film on a substrate. The active matrix LCDs enable display of animation with high resolution. Such high resolution animation is obtained with a TFT (Thin Film Transistor), which is a switching element of a matrix display portion, disposed on one of two substrates with a liquid crystal interposed between them.
In the typical manufacturing process for forming a high resolution LCD, the HTPS (high temperature polysilicon) having a high mobility of about 30 to 150 cm2/V·sec is used for the material of a channel layer in the TFT. When the polysilicon is used, the TFT is formed to have sufficient speed to be utilized as a driver in the LCD.
However, the polysilicon film is typically formed by a SPC (Solid Phase Crystallization) method that applies heat to an amorphous-silicon film formed on the substrate to induce crystallization or by a low pressure CVD method that directly deposits the polysilicon on the substrate. These film making methods are carried out at a high temperature of 700° C. to 900° C., so the polysilicon TFT LCD production process is called a high temperature process. In the high temperature process, an expensive substrate such as a heat-resistant quartz plate or the like is required, which leads to a high cost. Additionally, the size of the quartz plate has a limitation, which hinders the LCD from achieving large scale.